Geochronologic sequence of Neoproterozoic Tonian magmatism in Fanjingshan area, xiuning Country, Guizhou Province

In order to obtain the geochronologic sequence of the Neoproterozoic magmatism in Fanjingshan area of the western Jiangnan Orogen and to provide a reliable foundation of chronological study in the typical area for comprehensive comparison and for geopark declaration and science popularization, the paper reports the zircon U-Pb dating of a newly discovered diabase in Fanjingshan area. The result shows that the diabase was formed at 805.3±4.5Ma. The authors also sorted and summarized the existing age reports in a comprehensive and systematic way, and hold that the end of the eruption of basalts was 840Ma. There were two periods of basic-ultrabasic magmatism (831Ma, 814~805Ma) and two periods of acid magmatism (855Ma, 834Ma) that occurred in Fanjingshan area during Neoproterozoic. The magmatic geochronology sequence of Fanjingshan area largely corresponds to that of southwest Guizhou-north Guangxi area. Combined with rock types and its geochemical features, it is implied that the Neoproterozoic Early Tonian magmatic rocks in western part of Jiangnan Orogen were formed by the subduction-collision process of Yangtze and Cathaysia blocks, and the Late Tonian magmatic rocks were formed by the rifting process of South China Craton.